I am working on a project right now where I have to deal with an archaeological site that was first recorded by a man named Oscar Noren.
Noren was a rancher and farmer who lived in the San Joaquin Valley during the early 20th century, and who became interested in the native peoples of the area. He began to travel throughout the region, looking for archaeological sites, but also, importantly, getting to know the people of the area. He collected a huge amount of anthropological and archaeological data, organized it in a usable fashion, and left behind some excellent notes that are still used by archaeologists in the region, all without the benefit of any formal training in anthropology or archaeology. Noren's ties to the native community are solid, and he is still remembered fondly by the members of the community who interacted with him in their youths.
Most parts of California have someone like this - the avocational anthropologist who, out of sheer curiosity, was able to provide a base from which regional archaeologists, ethnographers, and ethnohistorians have since worked. Their reputations have fared differently depending on their methods and their approaches - those who tended to go digging without consultation with the Native communities have generally been though poorly of by both the Native peoples of their regions as well as by modern anthropologists; those who simply collected folklore and language information uncritically have provided a useful record, but one that can be very difficult to use as it often contains contradictory and confusing information; many were engaged in other ideological work that colored their view of what they were doing - I have read a few entries by itinerant preachers who also did amateur archaeology in the late 19th and early 20th century, and while they can provide very useful information, their disdain of the people whose remains they examined often shines through in not only the tone of their writings but also the information that they deem worth recording.
But, faults, and all, this work oftne provides information about both archaeology and ethnography which is not at all available today due to the effects of erosion, as well as cultural change. These accounts are greatly valuable.
Noren's work, which I have only recently become acquainted with, is particularly fascinating. From what I have seen so far, he seems more interested in observation and interaction with people than in deep interpretation, which makes his work very usable for a modern anthropologist. Moreover, because he made an effort to build and maintain ties with the Native San Joaquin community, I encounter people regularly who knew him and can fill in the occasional gaps in his information. It's really a fascinating exercise.
The modern equivalent of these folks is found in local archaeological societies and archaeological clubs - groups of people actually interested in the real past, who have a desire to read, study, record, and discuss their work in a solid, defensible way. While I know of nobody who currently has the ability to record the volume of information as these early avocationalists, mostly because of changes in land ownership to social norms, the spirit is still there, and it's something that I think needs to be nurtured.